Apart from the url mismatch, is this illegal? I don't think so, they are selling support for an opensource project. If this support is bad, not needed, ..., is more an ethical problem, but otherwise there is nothing wrong about it.
"Illegal" and "nothing wrong" aren't an exhaustive set.
Messing with Google will get you totally banned.
The phrase "terminate with prejudice," largely fallen into disuse today, means basically "fire this person and blacklist them from ever working here again". The variant "terminate with extreme prejudice" was popularized by the film Apocalypse Now and is a euphemism of sorts meaning "assassinate".
Basically implying (mostly tongue in cheek) that Google's retribution might go beyond just "terminate their AdWords account".
While charging for support isn't illegal in itself, a few cases have made their way through the courts, with the burned users not having to pay up as it's often not clear what the service you are paying for is even supposed to be. What is of course illegal (at least in Europe, I'd hope elsewhere too) is hiding the fact that they're charging for anything in the first place. The operators have cottoned on to this and will hide any mention of cost or a contract when you visit the page via a search engine or ad (based on the Referer [sic] header), but if you go back to the page directly after signing up or receiving a bill, it's all there. Obviously, they're trying to make you think you missed it first time around.
I suspect there is in theory also legal ground to fight this based on trademark, etc. grounds, but there's probably almost zero chance of real success, as it's way too easy to open a throwaway business that closes down the first sign of trouble.
The way to get at these guys is presumably proving them guilty of a criminal offence (fraud), in which case the business front won't help.
If you end up a victim of this sort of scam, basically categorically state (in writing) that you weren't aware you were agreeing to a contract, and that the contract is therefore void. Also, don't give them more info on you than they already have. If they send the bill by email and they don't have your physical address, don't send the refusal to pay in the mail with a return address, etc. They'll rarely try to hunt you down if you flat out refuse, there are unfortunately enough victims that will cough up as soon as they get a scary sounding letter with a legal-looking letterhead.
Mozilla could easily sue them for that alone.